POF helical structure: a non-contact approach for wide-range force measurements based on the coupling method

Abstract This study proposes a non-contact force-measuring sensor design that utilizes a polymer optical fiber. The sensor design uses two separate fibers (i.e. sensor input and sensor output fibers). The sensor input fiber is helically wound around a supportive circular pipe, with aim of creating bend losses at every bend loop. The sensor output fiber gains advantages by coupling the variable optical power from different bend loops of the sensor input fiber. The variable amount of optical power coupling is directly associated with the applied force on the spring, which serves as an intermediary in transferring force to the sensor. Further, for variable ranges of forces, three different springs are used, which sustain variable force ranges (0–20, 0–40 and 0–60 N), respectively. The proposed sensor design addresses the critical need for force sensors capable of effectively measuring force across a wide dynamic range. The results of this study support the sensor design, which has a wide range of force-measuring capabilities, from low to high, with a close and repeatable response. The low-range force measurement (0–20 N) indicates the sensor’s high sensitivity of 0.567 µW N −1 . Further, the sensor is also capable of a large force measuring range (0–60 N) with sensitivity of 0.189 µW N −1 .